Rotating screening devices are commonly used for separating solids from a fluid (i.e., defluidizing), drying solids, and applying powder coating(s) to the solids for pelletized polymers and/or tacky materials, sewage treatment, food processing, and the like. For example, a screening device may be used in lieu of a centrifugal dryer, which may be too rough on brittle materials, to remove the bulk of the fluid (e.g., water) from pellets (e.g., pelletized polymers and/or tacky materials) prior to additional drying, coating, and/or bagging. Alternatively, a screening device can be used downstream of another dryer to further dry the pellets or to coat the dried pellets with a powder that may help dry the pellets or prevent them from adhering to one another or to equipment during bagging.
Conventional screening devices typically include a hollow screening cylinder rotatably mounted on supporting rollers at a horizontal axis. A slurry of pellets and fluid is directed into an inlet end of the cylinder and flows through the cylinder as it rotates. Openings in the screen allow the fluid in the slurry to escape under the force of gravity, but retain and direct the pellets out of the cylinder at an outlet end. A dish placed under the outlet end catches the pellets as they exit the cylinder. In some designs, a housing surrounds the cylinder to shield the immediate area from undesired spray or exposure and to prevent contamination within the cylinder.
While helpful in defluidizing, drying, or coating pellets, these conventional screening cylinders may have several limitations. For instance, they may not effectively and adequately dry the pellets, and the remaining moisture may negatively alter the pellets' properties or result in misshaped pellets. Additionally, conventional screening cylinders may not efficiently dry the pellets, thereby requiring increased residence times or the use of multiple cylinders, and thus, delaying the drying and bagging process. The housing, while helpful in shielding sprays and preventing contamination, may make it difficult for an operator to observe activity within the cylinder and easily access the cylinder for maintenance or repairs. Further, as the screen(s) typically extend the entire length of the cylinder, conventional cylinders may not allow for classification of pellets based on size or shape, and may require additional expense for maintenance or repairs.
Accordingly, there is a need for improved systems and methods to address the above-mentioned deficiencies. Embodiments of the present disclosure are directed to these and other considerations.